g]), it accounts for an equal probability of experiencing terrestrial winds from all directions.
For Canada and the United States, a typical mean terrestrial wind speed ([U.
INFLUENCE OF TERRESTRIAL WINDS ON VEHICLE AERODYNAMICS
Terrestrial winds play an important role for the aerodynamics of ground vehicles.
Although the wind-averaged-drag approach accounts for variations in the mean terrestrial winds, turbulence associated with these winds and from the wakes of other vehicles on the road is usually not simulated in wind tunnel test programs.
The distinct shapes of these velocity profiles indicate that coast-down runs in opposite directions in the presence of terrestrial winds are different in character and ought to be treated as distinct objects of analysis.
A sensitivity analysis highlights the errors on the predicted free-stream speed and yaw angle that result from errors in the evaluation of the terrestrial wind speed and direction.
However, one major deviation of the proposed rule from standard J2263 is that the terrestrial wind velocity measured by track-based anemometers at vehicle mid-height is used to "calibrate" the vehicle-mounted anemometer sensing the apparent wind at a different height.
They discuss that drag reductions for commercial vehicles have been shown to be smaller in turbulent flows than smooth flows, implying that it may be more difficult to reduce the drag of HDVs in flow conditions representative of the turbulent terrestrial winds experienced on the road.
Terrestrial winds play an important role for the aerodynamics of road vehicles, but are often not replicated in a sufficient manner in wind tunnels.
Other more advanced techniques are available for calibrating the on-board wind measurement, such as the Taylor-hypothesis method implemented by Tanguay  which accounts for the advection of turbulence in the terrestrial winds.
The main differences between the sites are the local vegetation, which affects the terrestrial winds above to the road surface, and the track/road surface, which may influence the rolling resistance.